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Do I need calibration circuit for AD9744 to produce high-precision output?

Question asked by liubenyuan on Mar 12, 2017
Latest reply on Mar 13, 2017 by liubenyuan



I want to build a high precision arbitrary waveform generator using ad9744 and ad5683r. As agilent 33220A used ad9744, so I am planning to build my circuit using 33220a and ad9744 official references.


However, I found that there is a circuit in agilent 33220A, where it say that this circuit (U903B and Q901) are used to:


"The reference is V_AMPL from the System DAC circuit. The DAC
outputs two unipolar, complementary currents. U903b uses V_ AMPL
and buffer Q901 to subtract voltages from the two outputs to keep the
DAC output centered around 0 Volts."

I am confused about this circuit, especially the combination of opamp and pnp, 


1, What is the function or behavior of this circuit ? I assumed that V = Va - Vb is always centered around 0, is it right?

2, I found that in AD9744ACP-PCBZ RevB Schematic, no such circuit is used. So is this circuit needed for generating high precision outputs using AD9744?

3, Can AD9631 been used as a differential to unipolar conversion op-amp for AD9744?


Thanks !




1. Agilent 33220A waveform Schematic



2. AD9744 datasheet Figure 35.